The government of Prime Minister Shinzo Abe approved the new policy on Tuesday but has not announced when it will take effect, only saying that the measure could be introduced ahead of the summer season.
"The effective date of the implementation and the length of stay without visa will be announced soon," the Japanese embassy said on Tuesday.
The embassy advised Thai travellers to take heed of when the new rules come in, warning there will be no refunds for those visas issued before the waiver takes effect.
The embassy posted another statement on its website, saying that the government is working on the final touches for the implementation of the scheme, which could be launched this summer.
The policy is intended to bolster ties between the two countries. "We hope that the exchanges between Japan and Thailand will be further promoted by this visa relaxation," the Japanese government said in a statement.
Thai travel agents and travellers welcomed the visa exemption.
The Thai Travel Agents Association (TTAA) said it was confident that outbound tourism from Thailand to Japan will be boom this year.
Chumnong Tntharot, TTA vice president and managing director of Swadee Holiday Co, suggested the exemption would increase the sale of package tours to Japan at least 20-30% this year.
Japan is a popular destination for Thai tourists, ranking only behind Europe in popularity, he said, although more Thais visit China and South Korea because of they are cheaper.
The visa exemption, which will also be extended to Malaysia, is part of Japan's ambitious goal to see 10 million tourists visiting Japan this year and 30 million by 2020.
Kyodo News Agency reported government sources as saying that Japan was considering introducing multiple-entry visas for travellers from other Southeast Asian countries as well.
Wilawan Kosakarn, a businesswoman in Chanthaburi province, said the visa waiver will make it convenient for her to visit the country. She had planned to take a trip to Hokkaido soon, but has now postponed it until she can benefit from the visa change.